What is most likely true of an atom with a mass of 15 amu? there are 15 protons. there are 15 electrons. the total number of protons and electrons is 15. the total number of protons and neutrons is 15?

Option (c) is the correct answer.  

Explanation:

Mass number means the sum of total number of protons and total number of neutrons present in an atom.

For a neutral atom, the number of protons are equal to the number of electrons due to equal number of charges as protons are positively charged and electrons are negatively charged.

Thus, when an atom with a mass of 15 amu represents that the total number of protons and neutrons is 15.